This invention pertains to a method for the production and use of hydrogen donor solvents to increase the efficiency of processes to convert hydrocarbon residua feedstocks to lower boiling hydrocarbon liquid products.
It is well known that more hydrogen rich and lower boiling point hydrocarbon distillates can be produced from hydrogen deficient petroleum residua (resid) by thermally cracking in presence of a hydrogen donor diluent. U.S. Pat. No. 2,848,530 disclosed a process to produce lower boiling liquid hydrocarbons from a higher boiling hydrogen deficient petroleum oil by heat treatment in the presence of lower boiling point and partially hydrogenated aromatic-naphthenic diluent. Thermal tars, coal derived liquids, and catalytic cycle oils are preferred hydrogen donor diluent precursors.
U.S. Pat. No. 3,238,118 teaches the use of a gas oil hydrocracker to produce hydrogen donor diluent precursor. U.S. Pat. No. 4,090,947 teaches the use of a premium coker gas oil as the hydrogen donor precursor. U.S. Pat. No. 4,292,168 provides guidance on the desired hydrogen donor diluent properties using model compounds, but does not provide any guidance on commercially viable methods to produce a hydrogen donor diluent with the required properties. U.S. Pat. No. 4,363,716 teaches production of the hydrogen donor diluent precursor by contacting a gas oil stream with a molybdenum on alumina catalyst and hydrogen at 500 psia and 500° C. with a 0.5 hour residence time. One problem with all these processes is that the more aromatic hydrogen donor precursor is diluted with the less aromatic gas oil product from the hydrogen donor cracking product.
Other patents focused on increasing hydrogen donor process efficiency and maximum operable resid-to-distillates yield. U.S. Pat. No. 2,873,245 teaches the use of a second thermal cracking stage with catalytic cracking cycle (or decant) oil as make-up hydrogen donor diluent precursor. In a similar manner, U.S. Pat. No. 2,953,513 teaches the use of a second thermal cracking stage with a thermal tar hydrogen donor diluent precursor. U.S. Pat. No. 4,698,147 teaches the use of high temperature, short residence time operating conditions to increase the maximum resid conversion. U.S. Pat. No. 4,002,556 teaches the use of multiple point hydrogen donor diluent addition points to decrease the hydrogen requirement. U.S. Pat. Nos. 6,183,627 and 6,274,003 teach the use of a deasphalter to recover and recycle deasphalted oil to increase the maximum operable resid conversion to distillates by selectively removing coke precursors in the asphaltene product stream. U.S. Pat. No. 6,702,936 further increased the process efficiency by using partial oxidation of the asphaltene product to produce hydrogen for the hydrogen donor diluent cracking process.
U.S. Pat. No. 4,640,765 demonstrated that the addition of a hydrogen donor diluent to a batch ebullated bed hydrocracker increased the rate of residua conversion to distillates. Unfortunately, the addition of the hydrogen donor diluent also decreased the concentration of the residual oil in the ebullated bed hydrocracker. In a continuous ebullated hydrocracker, the adverse dilution effect is much greater than the beneficial effect of the more rapid resid conversion kinetics. As a result, efforts to increase the ebullated bed hydrocracker process maximum resid conversion and process efficiency have primarily focused on methods to selectively remove coke precursors from the reactor (U.S. Pat. Nos. 4,427,535; 4,457,830; and 4,411,768) and preventing coke precursors from precipitating in the process equipment (U.S. Pat. Nos. 4,521,295 and 4,495,060).
U.S. Pat. Nos. 5,980,730 and 6,017,441 introduced the concept of using a solvent deasphalter to remove coke precursors and recycle hydrotreated deasphalted oil to the ebullated bed resid hydrocracker. However, this process does not provide a method to control the hydrogen donor precursor properties required to produce an effective hydrogen donor solvent and recycles undesirable more paraffinic residual oil species to the ebullated bed resid hydrocracker. U.S. Pat. No. 5,228,978 teaches using a solvent deasphalting unit to separate the cracked resid product from an ebullated bed resid hydrocracker into an asphaltene coker feed stream, resin stream that is recycled to the ebullated bed resid hydrocracker, and more paraffinic residual oil stream that is fed to a conventional catalytic cracking unit. U.S. Pat. No. 4,686,028 teaches the use of a deasphalter to separate a resid oil feed into asphaltene, resin, and oil fractions and upgrading the resin fraction by visbreaking or hydrogenation.
Therefore, there remains a need for a practical means to effectively produce and use a hydrogen donor solvent in resid hydrocracking processes that has not been met by the prior processes.